1. Field of the Invention
The present invention relates generally to displacement measuring apparatus and, more particularly, is directed to a displacement measuring apparatus for detecting and measuring the amount of displacement of machine apparatus, inspection apparatus and the like.
2. Description of the Prior Art
A machine apparatus utilizes various kinds of scales to electrically measure the displacement amount of an object. The prior-art scale is large in size and is expensive, which limits the application field thereof. When the amount to be measured is relatively small, the displacement measuring apparatus making use of a differential transformer, as shown in FIG. 1, is frequently used. However, the displacement measuring apparatus using the differential transformer cannot overcome the following three shortcomings.
According to the first problem, coils 1 and 2 are coaxially disposed and a core 3 is movable through the inside of the coils 1 and 2. This makes the full length of the apparatus long as compared with the length of each of the coils 1 and 2, forming the differential transformer. Thus, the displacement measuring apparatus is not suitable to measure a large or long displacement.
According to the second problem, since the differential transformer is formed of the two coils 1 and 2 disposed in the axial direction, the total length of the two coils 1 and 2 is increased so that it is about three times the length of the displacement measuring range.
According to the third problem, the core 3 is movable through the insides of the two coils 1 and 2, and the core 3 is supported in a cantilever-fashion. Thus, the displacement measuring apparatus does not have the strength to resist vibration.